A conventional thermal printer has a printing tape having thermal fusible material disposed thereon positioned between a recording paper and a thermal head, a plurality of heat generating elements provided to the thermal head are selectively heated at successive printing positions during the movement of thermal head, and the data is printed on the recording paper by thermal transfer of the thermally fusible material of the printing tape. This thermal printer does not generates noise during the printing operation and it can print on conventional of recording paper.
In such conventional thermal printer, the thermal head is supported by the carriage which reciprocally moves along the platen and the tape cassette accommodating the printing tape is loaded to this carriage. In the reciprocal movement of the carriage, the printing is carried out only during movement of the thermal head in one direction, resulting in long periods where the thermal head does not print. Namely, during movement in the forward direction the thermal head pressingly contacts against the printing tape but disengages from pressurized contact with the tape when the carriage is returned.
Accordingly, printing is carried out only during the forward portion of the reciprocal movement of the carriage, but not in the return portion of the reciprocal movement of the carriage. Therefore, the printing speed is lowered because the return movement is not productively used to print and it is impossible to expect improvement in the printing efficiency.
The existing thermal printer described above is designed so that only one character, can be printed for given width of the printing tape and threfore it uses a large length of printing tape. As a result, the running cost becomes high and operation becomes uneconomical.
Because a large quantity of printing tape is used, the frequency of replacing the tape cassette accommodating the printing tape is high. Accordingly it is also impossible to expect improvement in the efficiency of printing using conventional thermal printers.
For eliminating the abovementioned disadvantages, another type of thermal printer, which prints two characters across the width of the printing tape, has also been proposed. In this case, both upper and lower parts of the printing tape are used for the printing regions. For example, after the printing over the total printing region of the upper part been completed, the tape cassette is lifted, the printing tape within this tape cassette is moved in the direction opposing to the preceding running direction, and the printing is then carried out on the unused printing region at the lower part.
This type of thermal printer is capable of reducing the quantity of printing tape used and the replacement frequency of the tape cassette as compared with the first-described thermal printer, but the printing is till carried out only during the forward portion of the reciprocal movement (double stroke movement) of the carriage. Accordingly, the printing speed is still the same as that of the existing thermal printer and improvement in the printing work efficiency cannot be expected.